The Illinois Waterway System is approximately 336 miles.  It extends from the mouth of the Calumet River to the mouth of the Illinois River at Grafton.  It provides a connection between the Great Lakes to the Missippi River.  A series of 8 locks control the flow of water from Lake Michigan.  The upper lock–T.J. O’Brien is 7 miles from Lake Michigan on the Calumet River.  The last lock is 90 miles upstream from the Mississippi River at the LaGrange lock and dam.  The other lock and dams in the system are: Lockport Lock and dam; Brandon Road Lock and dam(Joliet); Dresden Island Lock and dam( Morris); Marseilles Lock and dam; Starved Rock Lock and dam; Peoria Lock and dam.  The channel is maintained at 9 feet. At the O’Brien lock the waterway is 577 feet above sea level; at the LaGrange lock  it is 430 feet above sea level.
History
The Chicago Sanitary District was established in 1892 to create a solution to the recurrent sewage disposal problems plaguing the city. Basically water in Lake Michigan was contaminated with sewage from the Chicago River. The plan developed was to divert water from the lake and the Chicago River into a new canal. In 1892, work started on the Chicago Ship and Sanitary Canal. It’s goals were to improve transportation, dilute waste and move it downstream. The main channel opened in 1900. It was extended 3 miles downstream of Lockport in 1907. This was associated with the virtual closing of the Summit Division of the Illinois and Michigan Canal. A branch canal–the Cal Sag Canal was constructed between 1911–1922 between the Little Calumet River and the Chicago Sanitary and Ship Canal. This arrangement allowed some deep water shipping. But the new canal only extended to Joliet. Travel on the DesPlaines and Illinois Rivers was not dependable due to the fluctuating depths.
The Illinois General Assembly passed legislation authorizing the Illinois Waterway Project in 1919. This was to provide a channel between Lockport and Utica. This project was started by the State of Illinois; but was ultimately completed by the army Corps of Engineers in 1933. It’s completion resulted in the closure of the remaining Illinois Michigan Canal.

The Peoria Lock and Dam built in 1938 and the LaGrange Lock and Dam built 1936–9 were not part of the original Illinois Waterway Project.
They were built by the Army Corps of Engineers because of a Supreme Court decision limiting the amount of water that could be diverted from Lake Michigan into the Illinois Waterway.